Check out Jay Ham's article on sewing a SUL pack.
Click on the link below and click on number 3., LAB 2300 cu. in. Pack, under the listing backpacks. Then click on construction, followed by a click on Padded shoulder strap assembly.
There are plenty of pictures and instructions in both links. The second link also has instructions for a hip belt.
I hope this helps. :-)
Party On ! 2010